The vestibuloocular reflex (VOR) maintains clear vision during head movements. In development and aging, as well as in response to insult, the VOR must be continuously adjusted to promote clear vision. The inferior olive (IO) may be crucial for this adjustment, but its exact role is unclear. Indeed, we known very little about the function of the IO in any behavior. The proposed research will provide significant new information about the neural mechanisms of VOR adaptation and about IO function by studying IO cells in the dorsal cap (DC) and nucleus beta (N beta), structures which provide climbing fiber afferents to the cerebellar structures necessary for VOR adaptation. We will use monkeys because they are the best animal model for studying VOR adaptation. Their VOR is larger and adapts better than in other experimental species, and we can train their eye movements. We have three goals. First, we will characterize the signals that the IO relays to the vestibulocerebellum by recording from single cells in DC and N beta during a variety of visual, vestibular, and eye movement conditions. We will determine if these cells, like somatosensory IO cells, respond to unexpected, but not expected, sensory stimulation resulting from a movement. These results will tell us what conditions trigger IO's participation in eye movements. Second, we will describe the connections of the IO regions that participate in VOR adaptation. Results in rabbit suggest that different parts of DC and N beta receive different kinds of information and influence different directions of eye movement. Our anatomical work, in conjunction with our extracellular recording will determine if a similar organization exists in monkey. Third, we will evaluate the influence exerted by DC and N beta on the VOR and other eye movements by electrically stimulating or destroying these structures. Stimulation will determine if DC and N beta activity can elicit eye movements and if, as previously proposed, IO activity alters VOR gain when it is repeatedly paired with a vestibular stimulus. Destroying DC and N beta will determine how VOR adaptation depends on the information carried in DC and N beta. By characterizing the participation of the IO in VOR adaptation these studies will help us understand what the IO might contribute to motor adaptation in general and so will illuminate the neural mechanisms of motor adaptation occasioned by aging, trauma, or disease.